Mass- and energy- dependence of ($\pi^{+}$ $\pi^{-}$) double isobaric analog transitions at low energies

Anderl, Thomas

Book/Report

FZJ-2020-01859

Mass- and energy- dependence of ($\pi^{+}$ $\pi^{-}$) double isobaric analog transitions at low energies

Anderl, T. (Corresponding author)FZJ*

1988
Kernforschungsanlage Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Kernforschungsanlage Jülich GmbH Zentralbibliothek, Verlag, Spezielle Berichte der Kernforschungsanlage Jülich 429, 108 S. (1988)

Please use a persistent id in citations: http://hdl.handle.net/2128/24764

Report No.: Juel-Spez-0429

Abstract: Transitions to double isobaric analog states (DIAT) have beenmeasured in the double charge exchange (DCX) reaction ($\pi^{+}$ $\pi^{-}$) for thenuclei $^{26}$Mg, $^{56}$Fe at T$_{\pi}$+ = 49 MeV and for $^{18}$0 at T$_{\pi}$+ = 24 MeV, 33 MeV, 49 MeV, 64 MeV and 79 MeV for several angles. The experiments havebeen performed at the pion channels M13 and M11 of TRIUMF using thelow energy pion spectrometer QQD. The forward angle cross sectionsfor $^{18}$0 can be understood in a quark model as well as in conventionalmodels where the reaction is mainly proceeding through intermediatedeltas or low lying excited states of the intermediate nucleus. Theangular distribution of $^{26}$Mg at $^{49}$ MeV is found to be almost identicalto those of $^{14}$C and $^{18}$0 while the cross section remarkedly drops for$^{56}$Fe. The forward angle excitation function of $^{18}$0 exhibits a maximumat around 35 MeV. The present results are compared to theoreticalpredictions. Two approaches for a unified study of SCX and DCX atenergies ranging from 20 MeV up to 300 MeV are presented. The firstis carried out in a mean free path model for investigations ofgeometry effects in the reaction. For the second, the optical modelcode PIESDEX is employed. Both studies indicate that the observedmass dependence for DCX at 50 MeV can be explained partly by geometryconsiderations and partly by details in the nuclear matterdistributions of core neutrons and valence neutrons. Furthermore, theoptical model investigation reveals the$\pi$N-SCX amplitude down by 30 MeV in order to achieve good agreement with experimental data.need of shif ting the freeachieve good agreement

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